5-56 할리데이 11판 솔루션 일반물리학

$$\begin{cases} mg &= 2.0\ut{kN}\\ t&=6.0\ut{s}\\ v_0&=0\\ v&=88.5\ut{km/h}=\frac{295}{12}\ut{m/s}\\ g&=9.80665\ut{m/s^2} \end{cases}$$ $$\ab{a}$$ $$v=v_0+at,$$ $$\begin{aligned} a&=\frac{v-v_0}{t}\\ &=\frac{\frac{295}{12}-0}{6}\\ &=\frac{295}{72}\ut{m/s^2}\\ &\approx 4.097222222222222\ut{m/s^2}\\ &\approx 4.1\ut{m/s^2}\\ \end{aligned}$$ $$\ab{b}$$ $$\Sigma \vec F = m\vec a,$$ $$\begin{aligned} \Sigma F&=\frac{73750}{9g}\\ &\approx 835.6007856346912\ut{N}\\ &\approx 8.4\times10^2\ut{N}\\ \end{aligned}$$